1. Field of the Invention
The present invention relates to projection screens on which images are displayed by receiving light from a light source. In particular, the present invention relates to a reflective projection screen and a method for manufacturing the same.
2. Description of the Related Art
Overhead projectors and slide projectors have widely been used for showing materials in meetings and the like. Also, the use of video projectors and animation film projectors is spreading to ordinary households. In these projectors, light from a light source is spatially modulated to imaging light by a light valve, and the image light is projected onto a screen through an illumination optical system, such as a lens.
Some of this type of projectors can display color images and in which a lamp for emitting white light including three primary colors, which are red (R), green (G), and blue (B), is used as the light source and a transmissive liquid crystal panel is used as the light valve. In these projectors, white light emitted from a light source is divided into red light, green light, and blue light. Each color light is converged on a predetermined light path. These beams of light are spatially modulated by the liquid crystal panel, according to an image signal. The modulated light beams are synthesized to color image light in a photosynthesis portion. The synthesized color image light is magnified through a lens to be projected onto a projection screen.
Another type of projectors capable of displaying color images has recently been developed which includes a narrow-band three primary color light source, which may be a laser oscillator for emitting narrow-band light beams of three primary colors, and a grating light valve (GLV). In this projector, each color light beam emitted from the laser oscillator is spatially modulated by the GLV, according to image signals. The modulated light beams are synthesized to color image light in a photosynthesis portion, and the synthesized color image light is magnified through a lens to be projected onto a projection screen, as in the foregoing projector.
Screens used for the projectors are classified into the transmissive type and the reflective type. In a transmissive screen, projection light is emitted from the back side of the screen and viewed from the front. In a reflective screen, projection light is emitted from the front of the screen and the reflected light is viewed from the front. In either type, it is desired to form bright, high-contrast images in order to achieve a highly visible screen.
In front projectors using such a reflective projection screen, unfortunately, the reflection of external light cannot be suppressed by, for example, using a neutral density (ND) filter, in contrast to self-luminescent displays and rear projectors. In particular, it is difficult to increase the contrast on the projection screen in a bright environment.
In order to solve the problem, a projection screen 100 having an optical thin film 112 serving as a band-pass filter, as shown in FIG. 10, has been proposed in Japanese Patent Application Publication No. 2002-070799. The projection screen 100 includes a screen substrate 111 serving as a light absorber and the optical thin film 112 on the screen substrate 111. The optical thin film 112 is a dielectric multilayer laminate reflecting light in a specific wavelength band and transmitting at least visible light other than the light in the specific wavelength band. Each thickness of the layers of the dielectric laminate is set according to a simulation based on a matrix method. A light diffusion layer 113 for diffusing the light reflected from the optical thin film 112 is formed on the optical thin film 112. The light diffusion layer 113 is formed by arranging beads, using a film including a microlens array, and other common techniques.
In this projection screen 100, only light in a specific wavelength band of the light emitted from a projector is reflected from the optical thin film 112. This reflected light is diffused at the light diffusion layer 113 to form an image. On the other hand, the other light, emitted from the projector, is transmitted through the optical thin film 112 to be absorbed by the screen substrate 111. Since the optical thin film 112 serves as a band-pass filter to increase light/dark contrast, a distinct image can be displayed on the projection screen 100 even in a bright environment.
However, since the light diffusion layer 113 provides a viewing angle as small as 20°, the projection screen 100 cannot achieve satisfactory viewing characteristics.